function to calculate volume contained in the 'pools' in a two-dimensional array.

volume.js

function calculateVolume(heights) {
	var left = 0, right = 1, volume = 0;
	while (right < heights.length) {
		var level = heights[left];
		if (heights[right] <= level) {
			// tag the 'left cursor' along
			left = right;
			right = right + 1;
		} else {
			// walk to the left
			while (left >= 0 && heights[left] <= level) {
				left -= 1;
			}
			// over the edge, so no volume to be filled
			if (left < 0) {
				left = right;
				right += 1;
			} else {
				// add the volume to the total
				var distance = right - left;
				var peak = Math.min(heights[left], heights[right]);
				volume += (distance - 1) * (peak - level);	
			}
		}
	}
	return volume; 
}
document.write(calculateVolume([3,2,1,0,4]));
document.write("<br />");
document.write(calculateVolume([1,3,4,2,0,1,3,2,5,3]));
document.write("<br />");
document.write(calculateVolume([4,3,2,1,0,3]));

I think there should be a divide-and-conquer strategy to do this. But I'm not sure how.